Single-phase voltage source AC/DC converter and interconnection system

ABSTRACT

A single-phase voltage source AC/DC converter according to the present invention generates a second axis voltage command from difference between a DC voltage detection value at a DC terminal and a DC voltage command value and controls a DC voltage by increasing and decreasing active power with the second axis voltage command. For example, the voltage at the DC terminal is increased by decreasing active power when the DC voltage detection value at the DC terminal is lower than the DC voltage command, while the DC voltage detection value at the DC terminal is decreased by increasing the active power when the DC voltage detection value at the DC terminal is higher than the DC voltage command.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a single-phase voltage source AC/DCconverter capable of being applied to an interconnection device or anuninterruptible power source device being a power source of a powersystem and an interconnection system including the converter.

2. Description of the Related Art

There has been known a single-phase voltage source AC/DC convertercapable of supplying power as converting a direct current to analternating current by automatically adjusting a voltage, a frequencyand a phase to those of a power system which is to be connected with(for example, see Japanese Patent Application Laid-Open No.2009-219263).

SUMMARY OF THE INVENTION

A single-phase voltage source AC/DC converter of Japanese PatentApplication Laid-Open No. 2009-219263 operates such that power suppliedfrom a DC side is converted to an alternating current and is output to asystem as active power while power supplied from an AC side is convertedto a direct current and is output to the DC side as active power.

Here, it is required that a constant DC voltage is input to thesingle-phase voltage source AC/DC converter of Japanese PatentApplication Laid-Open No. 2009-219263.

Here, in a case that a DC device output DC voltage of which fluctuateslike recently-popularized solar power generation is directly connectedto the single-phase voltage source AC/DC converter of Japanese PatentApplication Laid-Open No. 2009-219263, it becomes difficult to controlAC output (i.e., a voltage, a frequency and a phase) when the DC voltageis decreased by a predetermined amount or more.

Meanwhile, there has been known an inverter capable of converting adirect current to an alternating current by controlling a fluctuating DCvoltage (for example, see “A Novel Utility-Interactive Electrical EnergyStorage System Making Use of Electrical Double-Layer Capacitors and anError Tracking Mode PWM Converter”, (The Institute of ElectricalEngineers of Japan, Industry Applications, Transactions, 118-12,December 1998)). FIG. 1 is a view illustrating an inverter described in“A Novel Utility-Interactive Electrical Energy Storage System Making Useof Electrical Double-Layer Capacitors and an Error Tracking Mode PWMConverter”, (The Institute of Electrical Engineers of Japan, IndustryApplications, Transactions, 118-12, December 1998). FIG. 2 is a viewillustrating details of an automatic voltage regulator (dc-AVR) inFIG. 1. A DC voltage command value V_(D)* being a target value of a DCterminal voltage is set at the inverter in FIG. 1. The automatic voltageregulator inputs a signal of difference between the DC voltage commandvalue V_(D)* and a DC voltage detection value V_(D) at the DC terminalto an amplifier having low pass characteristics. The automatic voltageregulator adds a DC current value at the DC terminal to the output ofthe amplifier (i.e., feedforward). Then, the automatic voltage regulatorobtains a PWM command j(t) as multiplying a signal obtained in afeedforward manner by a reference sine wave signal (i.e., a PCC voltage)which is systematically synchronized. The automatic voltage regulatorgenerates a gate signal based on the PWM signal j(t).

Here, since the difference between the detected DC voltage and thespecified value is provided in a feedforward manner as the PWM command,the inverter of “A Novel Utility-Interactive Electrical Energy StorageSystem Making Use of Electrical Double-Layer Capacitors and an ErrorTracking Mode PWM Converter” (The Institute of Electrical Engineers ofJapan, Industry Applications, Transactions, 118-12, December 1998) cannot perform autonomous parallel operation.

As described above, the single-phase voltage source AC/DC converter ofJapanese Patent Application Laid-Open No. 2009-219263 has a problem withinputting of a fluctuating DC voltage and the inverter of “A NovelUtility-Interactive Electrical Energy Storage System Making Use ofElectrical Double-Layer Capacitors and an Error Tracking Mode PWMConverter” (The Institute of Electrical Engineers of Japan, IndustryApplications, Transactions, 118-12, December 1998) has a problem ofincapability of autonomous parallel operation.

To address the above issues, the present invention provides asingle-phase voltage source AC/DC converter capable of freelycontrolling reactive power and performing autonomous parallel operationwhile being capable of supporting DC voltage fluctuation and aninterconnection system utilizing the single-phase voltage source AC/DCconverter.

In view of the above, the single-phase voltage source AC/DC converteraccording to the present invention controls a DC voltage by increasingand decreasing active power as generating a first axis command fromdifference between a measured reactive power value and a set reactivepower command value and generating a second axis voltage command fromdifference between the detected DC voltage and the set DC voltagecommand.

Specifically, a single-phase voltage source AC/DC converter according tothe present invention includes a single-phase voltage source AC/DCconverting circuit, which has internal equivalent impedance as seen froman AC terminal, for converting power from a DC voltage source connectedto a DC terminal to single-phase AC power to output from the AC terminalor for converting single-phase AC power from a single-phase AC sourceconnected to the AC terminal to DC power to output from the DC terminalin accordance with a pulse width of a gate signal generated based on aPWM command; a phase difference generating circuit, which has a phasedelay single-phase AC generator for delaying a phase of a single-phaseAC output voltage at the AC terminal and generating a delay single-phasealternating voltage, for generating a phase difference voltagecorresponding to phase difference between the single-phase AC outputvoltage at the AC terminal and an internal electromotive voltage of thesingle-phase voltage source AC/DC converting circuit based on the delaysingle-phase alternating voltage; a superior voltage control circuit towhich a first axis voltage command for amplitude of the single-phase ACoutput voltage at the AC terminal and a second axis voltage command fora single-phase AC frequency at the AC terminal are input for outputtinga voltage command signal generated so that the amplitude of thesingle-phase AC output voltage at the AC terminal approaches the firstaxis voltage command and a frequency command signal generated so thatthe single-phase AC frequency at the AC terminal approaches the secondaxis voltage command based on the first axis voltage command, the secondaxis voltage command, the phase difference voltage from the phasedifference generating circuit and the single-phase AC output voltage atthe AC terminal; a frequency control circuit for determining anelectrical angle of the internal electromotive voltage of thesingle-phase voltage source AC/DC converting circuit to generate agenerated electrical angle based on a reference frequency of asingle-phase AC output frequency at the AC terminal, the frequencycommand signal from the superior voltage control circuit, and an outputsignal from the phase difference generating circuit; a subordinatevoltage control circuit for outputting a signal generated so that theamplitude, the frequency, and the phase of the single-phase AC outputvoltage approach a synthesized value of a reference voltage of thesingle-phase AC output voltage at the AC terminal, the voltage commandsignal, and the generated electrical angle as the PWM command based onthe single-phase AC output voltage at the AC terminal, the generatedelectrical angle of the frequency control circuit, and the voltagecommand signal from the superior voltage control circuit; and a commandvalue arithmetic circuit to which a DC voltage command value to specifya voltage at the DC terminal is set and which obtains the second axisvoltage command by detecting a DC voltage detection value being thevoltage at the DC terminal and calculating difference between the DCvoltage command value and the DC voltage detection value.

The single-phase voltage source AC/DC converter according to the presentinvention generates a second axis voltage command from differencebetween a DC voltage detection value at a DC terminal and a DC voltagecommand value and controls a DC voltage by increasing and decreasingactive power with the second axis voltage command. For example, thevoltage at the DC terminal is increased by decreasing active power whenthe DC voltage detection value at the DC terminal is lower than the DCvoltage command, while the DC voltage detection value at the DC terminalis decreased by increasing the active power when the DC voltagedetection value at the DC terminal is higher than the DC voltagecommand.

A single-phase voltage source AC/DC converter is provided with twocommand values being a first axis voltage command V₁* and a second axisvoltage command V₂*. In a case of active power reactive power control(i.e., PQ control) of Japanese Patent Application Laid-Open No.2009-219263, an output signal of active control (i.e., P control) is asecond axis voltage command and an output signal of reactive control(i.e., Q control) is a first axis voltage command.

In the single-phase voltage source AC/DC converter according to thepresent invention, an output signal of DC voltage control is the secondaxis voltage command V₂* and an output signal of the reactive powercontrol (i.e., Q control) is the first axis voltage command V₁* asillustrated in FIG. 3, and then, the DC voltage and the reactive powerare concurrently controlled.

Accordingly, the present invention provides a single-phase voltagesource AC/DC converter capable of freely controlling reactive power andperforming autonomous parallel operation while being capable ofsupporting DC voltage fluctuation.

The command value arithmetic circuit of the single-phase voltage sourceAC/DC converter according to the present invention calculates thedifference between the DC voltage command value and the DC voltagedetection value with a low pass characteristic circuit.

Here, the low pass characteristic circuit of the command valuearithmetic circuit has characteristics of Equation 1.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack & \; \\{{{\hat{V}}_{2}^{*}(s)} = {{- \frac{K_{dc}}{1 + {T_{Kdc} \cdot s}}}\left( {{{\hat{V}}_{D}^{*}(s)} - {{\hat{V}}_{D}(s)}} \right)}} & (1)\end{matrix}$

where,

V₂* represents a second axis voltage command;

V_(D)* represents a DC voltage command value;

V_(D) represents a DC voltage detection value;

s represents a variable of laplace transform;

K_(dc) represents a proportional gain;

T_(Kdc) represents a first-order lag time constant; and

^ represents a laplace transform.

The command value arithmetic circuit of the single-phase voltage sourceAC/DC converter generates the second axis voltage command of thesingle-phase voltage source AC/DC converting circuit by performingamplifying after cutting a high frequency component of the differencebetween the DC voltage detection value and the DC voltage command valuewith the low pass character circuit. Here, even in a case that a highfrequency component is not cut with the low pass character circuit asthe first-order lag time constant T_(Kdc) being zero, the command valuearithmetic circuit can generate the second axis voltage command. Thecommand value arithmetic circuit has a better transient response than acommand value arithmetic circuit utilizing a later-mentioned integratingcircuit.

The command value arithmetic circuit of the single-phase voltage sourceAC/DC converter according to the present invention calculates thedifference between the DC voltage command value and the DC voltagedetection value with an integrating circuit.

The integrating circuit of the command value arithmetic circuit hascharacteristics of Equation 2.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack & \; \\{{{\hat{V}}_{2}^{*}(s)} = {{- \frac{1}{T_{dc} \cdot s}}\left( {{{\hat{V}}_{D}^{*}(s)} - {{\hat{V}}_{D}(s)}} \right)}} & (2)\end{matrix}$

where,

V₂* represents a second axis voltage command;

V_(D)* represents a DC voltage command value;

V_(D) represents a DC voltage detection value;

s represents a variable of laplace transform;

T_(dc) represents a integral time constant; and

^ represents a laplace transform.

The command value arithmetic circuit of the single-phase voltage sourceAC/DC converter generates the second axis voltage command of thesingle-phase voltage source AC/DC converting circuit by integrating thedifference between the DC voltage detection value and the DC voltagecommand value. The command value arithmetic circuit has a smaller DCvoltage deviation at a steady state than the command value arithmeticcircuit utilizing the low pass characteristic circuit described above.

The command value arithmetic circuit of the single-phase voltage sourceAC/DC converter according to the present invention calculates thedifference between the DC voltage command value and the DC voltagedetection value with a parallel circuit in which a low passcharacteristic circuit and an integrating circuit areparallely-arranged.

The parallel circuit of the command value arithmetic circuit hascharacteristics of Equation 3.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack & \; \\{{{\hat{V}}_{2}^{*}(s)} = {\left( {{- \frac{K_{dc}}{1 + {T_{Kdc} \cdot s}}} - \frac{1}{T_{dc} \cdot s}} \right)\left( {{{\hat{V}}_{D}^{*}(s)} - {{\hat{V}}_{D}(s)}} \right)}} & (3)\end{matrix}$

where,

V₂* represents a second axis voltage command;

V_(D)* represents a DC voltage command value;

V_(D) represents a DC voltage detection value;

s represents a variable of laplace transform;

K_(dc) represents a proportional gain;

T_(Kdc) represents a first-order lag time constant;

T_(dc) represents a integral time constant; and

^ represents a laplace transform.

Since the low pass characteristic circuit and the integrating circuitare parallely-arranged, the command value arithmetic circuit satisfiesboth of the transient response and the steady deviation.

The single-phase voltage source AC/DC converter according to the presentinvention further includes a DC current detecting circuit for detectinga DC current value at the DC terminal and the command value arithmeticcircuit adds the DC current value detected by the DC current detectingcircuit when calculating the difference between the DC voltage commandvalue and the DC voltage detection value. The single-phase voltagesource AC/DC converter according to the present invention can convergethe voltage at the DC terminal rapidly to the DC voltage command valueby forwardly feeding the DC current value.

Further, an interconnection system according to the present inventionincludes the single-phase voltage source AC/DC converter and n (n is anypositive integer) sets of DC devices which are connected to the DCterminal of the single-phase voltage source AC/DC converter via a DC/DCconverters so that DC power is transmitted to and received from the DCterminal.

The single-phase voltage source AC/DC converter is capable of performingautonomous parallel operation and controlling the DC voltage at adesired value. Accordingly, in the interconnection system, a DC energysource of which output voltage varies and a load can be connected to theDC terminal via the DC/DC converter while a power system is connected tothe AC terminal.

Accordingly, the present invention can provide the interconnectionsystem utilizing the single-phase voltage source AC/DC converter.

The present invention can provide a single-phase voltage source AC/DCconverter capable of freely controlling reactive power and performingautonomous parallel operation while being capable of supporting DCvoltage fluctuation and an interconnection system utilizing thesingle-phase voltage source AC/DC converter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a traditional inverter;

FIG. 2 is a view illustrating details of an automatic voltage regulator(dc-AVR);

FIG. 3 is a view illustrating concurrent control of a DC voltage andreactive power at a single-phase voltage source AC/DC converteraccording to the present invention;

FIG. 4 is a schematic configuration diagram of a single-phase voltagesource AC/DC converter according to the present invention;

FIG. 5 is a schematic configuration diagram of a single-phase voltagesource AC/DC converter according to the present invention;

FIG. 6 is a schematic configuration diagram of a single-phase voltagesource AC/DC converter according to the present invention;

FIG. 7 is a schematic configuration diagram of a single-phase voltagesource AC/DC converting circuit included in a single-phase voltagesource AC/DC converter according to the present invention;

FIG. 8 is a schematic configuration diagram of a single-phase voltagesource AC/DC converting circuit included in a single-phase voltagesource AC/DC converter according to the present invention;

FIG. 9 is a schematic configuration diagram of an AC power measuringinstrument included in a single-phase voltage source AC/DC converteraccording to the present invention;

FIG. 10 is a schematic configuration diagram of an AC power measuringinstrument included in a single-phase voltage source AC/DC converteraccording to the present invention;

FIG. 11 is a view illustrating connection relation of a control block ina single-phase voltage source AC/DC converter according to the presentinvention;

FIG. 12 is a schematic configuration diagram of a phase differencegenerating circuit included in a single-phase voltage source AC/DCconverter according to the present invention;

FIG. 13 is a view illustrating a command value arithmetic circuitincluded in a single-phase voltage source AC/DC converter according tothe present invention;

FIG. 14 is a view illustrating a command value arithmetic circuitincluded in a single-phase voltage source AC/DC converter according tothe present invention;

FIG. 15 is a view illustrating a command value arithmetic circuitincluded in a single-phase voltage source AC/DC converter according tothe present invention;

FIG. 16 is a view illustrating a command value arithmetic circuitincluded in a single-phase voltage source AC/DC converter according tothe present invention;

FIG. 17 is a view illustrating a command value arithmetic circuitincluded in a single-phase voltage source AC/DC converter according tothe present invention;

FIG. 18 is a view illustrating a command value arithmetic circuitincluded in a single-phase voltage source AC/DC converter according tothe present invention;

FIG. 19 is a view illustrating a configuration of an interconnectionsystem according to the present invention; and

FIG. 20 is a simulation result with a single-phase voltage source AC/DCconverter according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described with reference to theattached drawings. The embodiments hereinafter described are examples ofthe present invention, and the present invention is not limited to thefollowing embodiments. Meanwhile, components to which an identicalreference numeral is assigned in this description and the drawings areidentical to each other.

[Single-Phase Voltage Source AC/DC Converter]

FIG. 11 is a view exemplifying connection relation of a control block ina single-phase voltage source AC/DC converter and includes a superiorcommand vector B1, a superior control block B2, an ac-AVR block B3, anETM-PWM block B4, and a main switch B5. Regarding the ac-AVR block B3, atransformer connected to an output circuit of an inverter is preventedfrom anhysteretic magnetization by adopting a single-phase ac-AVR havinginternal equivalent impedance described in Japanese Patent ApplicationLaid-Open No. 2009-201224 as a main part of inductance. In addition,since the internal equivalent impedance can be actualized as a parallelcircuit of a resistance component and an inductance component, degree offreedom of design is increased.

A schematic configuration of a single-phase voltage source AC/DCconverter according to the present embodiment is illustrated in FIGS. 4and 5. Then, details of the respective blocks illustrated in FIG. 11 aredescribed.

A single-phase voltage source AC/DC converter 11 illustrated in FIG. 4includes a single-phase voltage source AC/DC converting circuit 40having internal equivalent impedance as seen from an AC terminal 22 forreceiving power at a DC terminal 21 from a DC voltage source (notillustrated) and converting to single-phase AC power in accordance witha pulse width of a gate signal generated based on a PWM command tooutput from the AC terminal 22; a phase difference generating circuit 30having a phase delay single-phase AC generator to generate a delaysingle-phase alternating voltage of which phase is delayed against asingle-phase AC output voltage at the AC terminal 22 for generating aphase difference voltage corresponding to phase difference between thesingle-phase AC output voltage at the AC terminal 22 and an internalelectromotive voltage of the single-phase voltage source AC/DCconverting circuit 40 based on the delay single-phase alternatingvoltage;

a power control circuit 150 which outputs a first axis voltage commandvalue 120-1 to control amplitude of the single-phase output voltage atthe AC terminal 22 and a second axis voltage command value 120-2 tocontrol a frequency of the single-phase output voltage at the ACterminal 22 so that a DC voltage at the DC terminal 21 approaches a DCvoltage command value and a reactive power value of the single-phaseoutput power at the AC terminal 22 approaches a reactive power commandvalue based on the DC voltage command value specifying a voltage at theDC terminal 21, the reactive power command value against the reactivepower value of the single-phase output power at the AC terminal 22, a DCvoltage detection value obtained by detecting a voltage at the DCterminal 21, and a reactive power measurement value of the single-phaseoutput power at the AC terminal 22;

a superior voltage control circuit 70 which outputs a voltage commandsignal and a frequency command signal generated so that the amplitudeand the frequency of the single-phase AC output voltage at the ACterminal 22 respectively approach the first axis voltage command value120-1 and the second axis voltage command value 120-2 based on the firstaxis voltage command value 120-1 and the second axis voltage commandvalue 120-2 from the power control circuit 150, the phase differencevoltage from the phase difference generating circuit 30, and thesingle-phase AC output at the AC terminal 22;

a frequency control circuit 50 which generates a generated electricalangle based on a reference frequency of a single-phase AC outputfrequency at the AC terminal 22, the frequency command signal from thesuperior voltage control circuit 70, and the phase difference voltagefrom the phase difference generating circuit 30 and which synchronizesan electrical angle of an internal electromotive voltage of thesingle-phase source AC/DC converting circuit 40 with the generatedelectrical angle; and

a subordinate voltage control circuit 60 which outputs a signalgenerated so that the amplitude, the frequency, and the phase of thesingle-phase output voltage approach a synthesized value of thereference voltage of the single-phase AC output voltage at the ACterminal 22, the voltage command value and the generated value as thePWM command based on the single-phase AC output voltage at the ACterminal 22, the generated value from the frequency control circuit 50,and the voltage command signal from the superior voltage control circuit70.

The first axis voltage command value 120-1 and the second axis voltagecommand value 120-2 correspond to the superior command vector B1 in FIG.11. The superior voltage control circuit 70 corresponds to the superiorcontrol block B2 in FIG. 11. The subordinate voltage control circuit 60and the frequency control circuit 50 correspond to the ac-AVR block B3in FIG. 11. A gate signal generator 41 corresponds to the ETM-PWM blockB4 in FIG. 11. A single-phase voltage source AC/DC converting unitincluded in the single-phase voltage source AC/DC converting circuit 40corresponds to the main switch B5 in FIG. 11.

The single-phase voltage source AC/DC converting circuit 40 convertspower from the DC voltage source (not illustrated) to single-phase ACpower in accordance with the pulse width of the gate signal generated bythe gate signal generator 41 based on the PWM command. Examples of theDC voltage source include a voltage source such as a battery to output aDC voltage independently, a voltage source to output a DC voltage asrectifying after generating power with a power generating method such aspower generation by wind, and a voltage source to output a DC voltage bycontrolling a voltage of a DC capacitor. Here, it is also possible thata blocking inductor is further provided between a connection point of anoutput voltage detecting circuit 31 and the AC terminal 22 and eachsingle-phase AC output voltage is output from the AC terminal 22 throughthe blocking inductor. In this case, it is possible to prevent outflowof a PWM component to the AC terminal 22 at the single-phase voltagesource AC/DC converting circuit 40.

Schematic configuration diagrams of the single-phase voltage sourceAC/DC converting circuit are illustrated in FIGS. 7 and 8.

A single-phase voltage source AC/DC converting circuit 40-1 illustratedin FIG. 7 includes a single-phase voltage source AC/DC converting unit42 having internal equivalent impedance as seen from the AC terminal 22to receive power from the DC voltage source at the DC terminal 21 inaccordance with the pulse width of the gate signal and to output afterconverting to single-phase AC power, a current detecting circuit 43which detects a single-phase AC output current of the single-phasevoltage source AC/DC converting unit 42 and outputs a signal generatedcorresponding to magnitude of the single-phase AC output current, thegate signal generator 41 which generates and outputs the gate signal sothat difference between the PWM command and the output from the currentdetecting circuit 43 approaches zero, and a single-phase AC filtercircuit 45 which outputs as removing a high frequency component causedby the gate signal at the single-phase voltage source AC/DC convertingunit 42 from the single-phase AC output voltage of the single-phasevoltage source AC/DC converting unit 42.

Further, instead of the current detecting circuit 43 in FIG. 7, asingle-phase voltage source AC/DC converting circuit 40-2 illustrated inFIG. 8 includes a voltage detecting circuit 44 which detects asingle-phase AC output voltage of the single-phase voltage source AC/DCconverting unit 42 and outputs a signal generated corresponding tomagnitude of the single-phase AC output voltage. In this case, the gatesignal generator 41 generates and outputs the gate signal so thatdifference between the PWM command and the output from the voltagedetecting circuit 44 approaches zero.

The internal equivalent impedance included in the single-phase voltagesource AC/DC converting unit 42 illustrated in FIGS. 7 and 8 can beadded by control variables in the single-phase voltage source AC/DCconverter 11 in FIG. 4 or by connecting a resistance, a reactor, asingle-phase transformer or a combination thereof to the output of thesingle-phase voltage source AC/DC converting circuit 40-1, 40-2 in FIGS.7 and 8. For example, it is possible to serially connect a resistance ora reactor to each single-phase output of the single-phase voltage sourceAC/DC converting circuits 40-1, 40-2. Here, in the case that aresistance is connected, it is also possible to serially connect areactor subsequently to the resistance. Further, it is also possible toconnect a single-phase transformer to a single-phase output of thesingle-phase voltage source AC/DC converting circuits 40-1, 40-2. Here,in the case that a reactor is connected to each single-phase output ofthe single-phase voltage source AC/DC converting circuits 40-1, 40-2, itis also possible to connect a single-phase transformer subsequently tothe reactor. Further, in the case that a resistance is connected to eachsingle-phase output of the single-phase voltage source AC/DC convertingcircuits 40-1, 40-2 and a reactor is serially connected subsequently tothe resistance, it is also possible to connect a single-phasetransformer subsequently to the reactor. In this manner, by allowing thesingle-phase voltage source AC/DC converting circuit 40 to have theinternal equivalent impedance, the single-phase voltage source AC/DCconverter 11 in FIG. 4 can operate as a voltage source as beingconnected to a power system.

When the single-phase voltage source AC/DC converting circuit 40 in FIG.4 is structured as illustrated in FIG. 7 or FIG. 8, the single-phasevoltage source AC/DC converter 11 can remove a high frequency componentcaused by the gate signal at the single-phase voltage source AC/DCconverting unit 42 from the output of the single-phase voltage sourceAC/DC converting unit 42 owing to being provided with the single-phaseAC filter circuit 45 (as in FIGS. 7 and 8). Further, since the currentor the voltage from the single-phase voltage source AC/DC convertingunit 42 is detected at the current detecting circuit 43 or the voltagedetecting circuit 44 and the gate signal is generated at the gate signalgenerator 41 so that the difference between the PWM command and theoutput from the current detecting circuit 43 or the voltage detectingcircuit 44 approaches zero, it is possible to control current errors tobe within an allowable range or to control the output voltage to followthe PWM command.

The output voltage detecting circuit 31 in FIG. 4 detects thesingle-phase AC output voltage at the AC terminal 22 and outputs to thephase difference generating circuit 30, the subordinate voltage controlcircuit 60, and the superior voltage control circuit 70 respectively.Here, it is also possible that a low pass filter is arrangedantecedently to the output voltage detecting circuit 31 to detect thesingle-phase AC output voltage to the output voltage detecting circuit31 via the low pass filter. It is possible to stabilize control of thesingle-phase voltage source AC/DC converter 11 as removing the PWMcomponent from the single-phase AC output voltage. Further, it is alsopossible that a low pass filter is arranged subsequently to the outputvoltage detecting circuit 31 to output the output voltage from theoutput voltage detecting circuit 31 via the low pass filter. It ispossible to stabilize control of the single-phase voltage source AC/DCconverter 11 as removing the PWM component from the output voltage fromthe output voltage detecting circuit 31.

An output current detecting circuit 34 in FIG. 4 detects a single-phaseAC output current at the AC terminal 22 via a current transformer 38 andoutputs to an AC power measuring instrument 140.

The phase difference generating circuit 30 in FIG. 4 generates the phasedifference voltage corresponding to the phase difference between thesingle-phase AC output voltage V_(FIL)(t) at the AC terminal 22 and theinternal electromotive voltage of the single-phase voltage source AC/DCconverting circuit 40. FIG. 12 illustrates an example of a schematicconfiguration diagram of the phase difference generating circuit 30. Thephase difference generating circuit 30 includes a phase delaysingle-phase AC generator 35 to generate delay single-phase alternatingvoltage of which specified phase is delayed from single-phase AC voltageinput from a terminal 33-1, a phase difference voltage generator 36 togenerate the phase difference voltage from the single-phase AC voltageinput from the terminal 33-1, a voltage of the delay single-phasealternating voltage from the phase delay single-phase AC generator 35and a value input from a terminal 33-3, and a terminal 33-2 to outputthe phase difference voltage. In FIG. 12, the phase delay single-phaseAC generator 35 delays the phase of the delay single-phase alternatingvoltage approximately by 90 degrees. Here, the delayed phase may be anyangle as long as not being 0 degree or 180 degrees.

The single-phase AC output voltage V_(FIL) (t) detected by the outputvoltage detecting circuit 31 is input to the terminal 33-1. A generatedelectrical angle 57 generated by the later-mentioned frequency controlcircuit 50 is input to the terminal 33-3. The single-phase AC outputvoltage V_(FIL)(t) at the AC terminal 22 is expressed by Equation 5.[Equation 5]V _(FIL)(t)=√{square root over (2)}E _(s)·sin(ω_(S) t+θ _(S))  [V]

Where, ω_(s), θ_(s), and E_(s) respectively represent an angularfrequency (rad/s), a phase angle (rad), and an effective value (V). Areference of the phase angle is based on the internal electromotivevoltage.

In a case that the angular frequency ω_(s) of the single-phase AC outputvoltage at the AC terminal 22 and a reference angular frequency ω_(co)of the single-phase voltage source AC/DC converting circuit 40 areequal, phase difference between the single-phase AC output voltageV_(FIL)(t) and a phase delay single-phase AC voltage V″_(FIL) (t)becomes to 90 degrees and the phase delay single-phase AC voltageV″_(FIL)(t) to be generated by the phase delay single-phase AC generator35 is expressed by Equation 6.

$\begin{matrix}\begin{matrix}{{V_{FIL}^{''}(t)} = {V_{FIL}\left( {t - \frac{\pi}{2\;\omega_{co}}} \right)}} \\{= {\sqrt{2}{E_{s} \cdot {\sin\left( {{\omega_{s}t} + \theta_{s} - \frac{{\pi\omega}_{s}}{2\;\omega_{co}}} \right)}}}} \\{= {{- \sqrt{2}}{E_{s} \cdot {\cos\left( {{\omega_{s}t} + \theta_{s}} \right)}}}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

The phase difference voltage generator 36 outputs a phase differencevoltage V_(q)(t) from the single-phase AC output voltage V_(FIL)(t), thephase delay single-phase AC voltage V″_(FIL)(t), and the generated valuegenerated by the frequency control circuit 50. The phase differencevoltage V_(q)(t) is expressed by Equation 7.

$\begin{matrix}\begin{matrix}{{V_{q}(t)} = {{{{V_{FIL}(t)} \cdot \cos}\;\theta_{i}} + {{{V_{FIL}^{''}(t)} \cdot \sin}\;\theta_{i}}}} \\{= {\sqrt{2}E_{s}\left\{ {{\sin\left( {{\omega_{s}t} + \theta_{s} - \theta_{i}} \right)} + {\frac{\pi\left( {\omega_{co} - \omega_{s}} \right)}{2\;\omega_{co}}{\sin\left( {{\omega_{s}t} + \theta_{s}} \right)}\sin\;\theta_{i}}} \right\}}} \\{= {\sqrt{2}{E_{s} \cdot {\sin\left( {{\omega_{s}t} + \theta_{s} - \theta_{i}} \right)}}}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

When angular velocity of θ_(i) is equal to ω_(s), Equation 3 becomes toa constant value. As being phase difference between voltages at bothends of the internal equivalent impedance, θ_(s) is small generally.Accordingly, V_(q)(t) can be approximated as Equation 8.V _(q)(t)=√{square root over (2)}E _(s)·θ_(s)  [Equation 8]

The phase difference generating circuit 30 outputs the generated phasedifference voltage to the frequency control circuit 50 and the superiorvoltage control circuit 70 respectively. In the above, only a case thatω_(s) and ω_(co) are equal is described. However, even in a case ofbeing not equal, it is possible to acquire a similar approximatesolution and there is no practical problem.

The frequency control circuit 50 determines the electrical angle of theinternal electromotive voltage of the single-phase voltage source AC/DCconverting circuit 40 based on the reference frequency of thesingle-phase AC output frequency at the AC terminal 22, the frequencycommand signal from the superior voltage control circuit 70, and theoutput signal from the phase difference generating circuit 30.Specifically, as illustrated in FIG. 5, a second adder 56 adds thefrequency command signal from the superior voltage control circuit 70and the phase difference voltage from the phase difference generatingcircuit 30. A loop filter 53 filters a low range component being acomponent related to the frequency difference of the single-phase ACoutput voltage to the frequency component of the signal output by thesecond adder 56. A low pass element added by the loop filter 53 is adelay element such as a primary delay element, for example. Accordingly,the feedback loop can be stabilized.

Further, a third adder 58 adds the reference frequency output from areference frequency setting unit 51 and an output value of the loopfilter 53. A temporal integrator 55 performs temporal integration to theoutput from the third adder 58. The generated electrical angle 57 withan inherent angle θ_(i) is obtained by the temporal integration on theoutput from the third adder 58 performed by the temporal integrator 55.

The generated electrical angle 57 becomes to the electrical angle of theinternal electromotive voltage of the single-phase voltage source AC/DCconverting circuit 40 by a second multiplier 65 of the subordinatevoltage control circuit 60. Accordingly, it is possible to allow therotational angle to follow the frequency of the power system.

Here, the phase difference generating circuit 30 outputs the phasedifference voltage corresponding to the phase difference between thesingle-phase AC output voltage at the AC terminal 22 and the internalelectromotive voltage of the single-phase voltage source AC/DCconverting circuit 40 as described above. Therefore, the signal processin the phase difference generating circuit 30 is considered tocorrespond to the phase comparison process to compare the phases of thesingle-phase AC output voltage and the generated electrical angle 57from the frequency control circuit 50. Further, the signal process toperform integration after adding the reference frequency from thereference frequency setting unit 51 and the output value from the loopfilter 53 is considered to correspond to the signal process of thevoltage controlled oscillator (VCO) which varies a value of thegenerated electrical angle 57 in accordance with the output voltage fromthe loop filter 53. Therefore, the phase difference generating circuit30 and the frequency control circuit 50 are considered to perform theoperation as the PLL as a whole in which the generated electrical angle57 is synchronized with frequency of the single-phase AC output voltageat the AC terminal 22.

The first axis voltage command value 120-1 and the second axis voltagecommand value 120-2 from the later-mentioned power control circuit 150,the generated electrical angle 57 from the frequency control circuit 50,the phase difference voltage from the phase difference generatingcircuit 30, and the single-phase AC output voltage at the AC terminal 22are input to the superior voltage control circuit 70 in FIG. 4. Based onthe above inputs, the superior voltage control circuit 70 outputs thevoltage command signal and the frequency command signal generated sothat the amplitude and the frequency of the single-phase AC outputvoltage at the AC terminal 22 approach the first axis voltage commandvalue 120-1 and the second axis voltage command value 120-2. It is alsopossible to input the first axis voltage command value 120-1 and thesecond axis voltage command value 120-2 to the superior voltage controlcircuit 70 not directly but via a limiter 121 which defines an superiorlimit and a subordinate limit of the first axis voltage command value120-1 and the second axis voltage command value 120-2. Specifically, asillustrated in FIG. 5, a first multiplier 73 multiplies a value obtainedby multiplying J2 by a sine wave of the generated electrical angle 57from the frequency control circuit 50 by the first axis voltage commandvalue 120-1. A first subtracter 71 a subtracts the AC output voltage atthe AC terminal 22 from the signal from the first multiplier 73. A firstsuperior control amplifier 72 a amplifies the signal from the firstsubtracter 71 a to output as the voltage command signal so that thesingle-phase AC output voltage at the AC terminal 22 approaches thefirst axis voltage command value 120-1. Further, a second subtracter 71b subtracts the phase difference voltage from the phase differencegenerating circuit 30 from a value obtained by multiplying √2 by thesecond axis voltage command value 120-2. A second superior controlamplifier 72 b amplifies the signal from the second subtracter 71 b tooutput as the frequency command signal so that the frequency of thesingle-phase AC output voltage at the AC terminal 22 approaches thesecond axis voltage command value 120-2.

Accordingly, even when the amplitude and the frequency of the powersystem are varied, the respective errors of the amplitude and thefrequency of the single-phase output power of the single-phase voltagesource AC/DC converter 11 against the amplitude and the frequency can bedetected. Here, the first superior control amplifier 72 a and the secondsuperior control amplifier 72 b may add the low pass element to theoutput from the first subtracter 71 a and the second subtracter 71 b.Accordingly, the feedback loop can be stabilized. Further, it is alsopossible to further provide the limiter subsequently to the firstsuperior control amplifier 72 a and the second superior controlamplifier 72 b and output the outputs from the first superior controlamplifier 72 a and the second superior control amplifier 72 b via thelimiter. It is possible to prevent the excessive output to stabilize thecontrol.

The subordinate voltage control circuit 60 in FIG. 4 outputs the signalgenerated so that the amplitude, the frequency, and the phase of thesingle-phase AC output voltage approach the synthesized value of thereference voltage of the single-phase AC output voltage at the ACterminal 22, the voltage command signal, and the electrical anglecommand signal as the PWM command based on the single-phase AC outputvoltage at the AC terminal 22, the electrical angle command signalincluding the generated electrical angle 57 of the frequency controlcircuit 50, and the voltage command signal from the superior voltagecontrol circuit 70. Here, the reference voltage is previously set by areference voltage setting unit 61. The reference voltage becomes to thereference of the amplitude of the single-phase AC output voltage at theAC terminal 22.

Specifically, as illustrated in FIG. 5, the reference voltage settingunit 61 sets and outputs the reference voltage. The second multiplier 65multiplies the value obtained by multiplying J2 by the sine value of thegenerated electrical angle 57 from the frequency control circuit 50 bythe reference voltage from the reference voltage setting unit 61. Afirst adder 62 outputs after adding the voltage command signal from thesuperior voltage control circuit 70 and the signal output from thesecond multiplier 65. A third subtracter 63 subtracts the signal fromthe output voltage detecting circuit 31 from the signal output by thefirst adder 62. The voltage controller 64 controls the signal output bythe third subtracter 63 so that the single-phase AC output voltage atthe AC terminal 22 approaches the synthesized value of the referencevoltage, the voltage command signal, and the electrical angle commandsignal to output as the PWM command.

Accordingly, it is possible to compensate the error detected by thesuperior voltage control circuit 70 and to control the amplitude and thephase of the single-phase voltage source AC/DC converter 11 so that theamplitude and the phase of the single-phase AC output voltage of thesingle-phase voltage source AC/DC converter 11 is matched with theamplitude and the phase of the power system. For example, an amplifiermay be adopted as the voltage controller 64. Here, it is also possiblethat a low pass filter is further provided between the third subtracter63 and the voltage controller 64 and that the output from the thirdsubtracter 63 is output via the low pass filter. It is possible tostabilize the control by the voltage controller 64. Further, it is alsopossible that the voltage limiter is provided between the thirdsubtracter 63 and the voltage controller 64 (when the low pass filter isprovided on this position, between the low pass filter and the voltagecontroller 64) and that the output from the third subtracter 63 isoutput via the voltage limiter. Transient variation of the outputvoltage at the time of activation of the single-phase voltage sourceAC/DC converter 11 can be inhibited.

The AC power measuring instrument 140 in FIG. 4 receives inputs of thevalue of the single-phase AC output voltage at the AC terminal 22detected by the output voltage detecting circuit 31 and the value of thesingle-phase AC output current at the AC terminal 22 detected by theoutput current detecting circuit 34, and then, calculates a value ofactive power and a value of reactive power of the single-phase outputpower at the AC terminal 22.

Specifically, as illustrated in FIG. 9, in the AC power measuringinstrument 140, a product of the voltage and the current at a powermeasuring point measured respectively by the output voltage detectingcircuit 31 and the output current detecting circuit 34 multiplied at amultiplier 147-1 is passed through a low pass filter 149-1 and theactive power value is measured at an active power value measuringcircuit 145. Further, a function of which current phase at the powermeasuring point is shifted by 90 degrees by a current phase delayingcircuit 143 is generated. Then, a product of the function and thevoltage at the power measuring point multiplied at a multiplier 147-2 ispassed through a low pass filter 149-2 and the reactive power value ismeasured by a reactive power value measuring circuit 146.

Alternatively, the AC power measuring instrument 140 may be structuredas illustrated in FIG. 10. The AC power measuring instrument 140includes a reference frequency circuit 141 which generates a referencefrequency, a voltage phase delaying circuit 142 which generates adelayed AC voltage as delaying the phase of the measured AC voltagebeing the AC voltage at the power measuring point based on the referencefrequency from the reference frequency circuit 141, a current phasedelaying circuit 143 which generates a delayed AC current as delayingthe phase of the measured AC current being the AC current at the powermeasuring point based on the reference frequency from the referencefrequency circuit 141, and a power arithmetic circuit 144. In the powerarithmetic circuit 144, a product of the measured AC voltage and themeasured AC current multiplied at the multiplier 147-1 and a product ofthe delayed AC voltage from the voltage phase delaying circuit 142 andthe delayed AC current from the current phase delaying circuit 143multiplied at the multiplier 147-2 are added by an adder 148-1. Then,the sum is passed through the low pass filter 149-1 to be measured asthe active power value by the active power value measuring circuit 145.Further, a product of the measured AC voltage and the delayed AC currentfrom the current phase delaying circuit 143 multiplied at a multiplier147-3 is subtracted at a subtracter 148-2 from a product of the measuredAC current and the delayed AC voltage from the voltage phase delayingcircuit 142 multiplied at a multiplier 147-4. The difference is passedthrough a low pass filter 149-2 and the reactive power value is measuredby the reactive power value measuring circuit 146. By adding the productof the delayed AC voltage and the delayed AC current to the product ofthe measured AC voltage and the measured AC current, a double frequencycomponent included in the active power value can be decreased. Further,by subtracting the product of the measured AC voltage and the delayed ACcurrent from the product of the measured AC current and the delayed ACvoltage, a double frequency component included in the reactive powervalue can be decreased. Accordingly, the active power value and thereactive power value can be controlled accurately as improvingmeasurement accuracy of the active power value and the reactive powervalue.

The power control circuit 150 in FIG. 4 receives inputs of the DCvoltage command value against the DC voltage at the DC terminal 21, thereactive power command value against the reactive power value of thesingle-phase output power at the AC terminal 22, the DC voltagedetection value at the DC terminal 22 detected by a DC voltage detectingcircuit 161, and the reactive power value of the single-phase outputpower at the AC terminal 22 calculated by the AC power measuringinstrument 140. The power control circuit 150 generates and outputs thefirst axis voltage command value 120-1 against the amplitude of thesingle-phase output voltage at the AC terminal 22 and the second axisvoltage command value 120-2 against the frequency thereof so that the DCvoltage at the DC terminal 21 approaches the DC voltage command valueand the reactive power value of the single-phase output power at the ACterminal 22 approaches the reactive power command value.

FIG. 3 is a block diagram illustrating control details of the powercontrol circuit 150. The power control circuit 150 calculates differencebetween the reactive power command value and the reactive power value atan adding circuit 153 and outputs the first axis voltage command valueas calculating at a command value arithmetic circuit 151. Further, thepower control circuit 150 calculates difference between the DC voltagecommand value and the DC voltage detection value at an adding circuit154 and outputs the second axis voltage command value as calculating ata command value arithmetic circuit 152.

FIGS. 13 to 15 are views illustrating arithmetic at the command valuearithmetic circuit 152. The command value arithmetic circuit 152 in FIG.13 calculates the difference between the DC voltage command value andthe DC voltage detection value with a low pass characteristic circuit152 a. The low pass characteristic circuit 152 a has characteristics ofEquation 1.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack & \; \\{{{\hat{V}}_{2}^{*}(s)} = {{- \frac{K_{dc}}{1 + {T_{Kdc} \cdot s}}}\left( {{{\hat{V}}_{D}^{*}(s)} - {{\hat{V}}_{D}(s)}} \right)}} & (1)\end{matrix}$

where,

V₂* represents a second axis voltage command;

V_(D)* represents a DC voltage command value;

V_(D) represents a DC voltage detection value;

s represents a variable of laplace transform;.

K_(dc) represents a proportional gain;

T_(Kdc) represents a first-order lag time constant; and

^ represents a laplace transform.

The command value arithmetic circuit 152 in FIG. 14 calculates thedifference between the DC voltage command value and the DC voltagedetection value with an integrating circuit 152 b. The integratingcircuit 152 b has characteristics of Equation 2.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack & \; \\{{{\hat{V}}_{2}^{*}(s)} = {{- \frac{1}{T_{dc} \cdot s}}\left( {{{\hat{V}}_{D}^{*}(s)} - {{\hat{V}}_{D}(s)}} \right)}} & (2)\end{matrix}$

where,

V₂* represents a second axis voltage command;

V_(D)* represents a DC voltage command value;

V_(D) represents a DC voltage detection value;

s represents a variable of laplace transform;

T_(dc) represents a integral time constant; and

^ represents a laplace transform.

The command value arithmetic circuit 152 in FIG. 15 calculates thedifference between the DC voltage command value and the DC voltagedetection value with a parallel circuit 152 c in which the low passcharacteristic circuit 152 a and the integrating circuit 152 b areparallely-arranged. The parallel circuit 152 c has characteristics ofEquation 3.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack & \; \\{{{\hat{V}}_{2}^{*}(s)} = {\left( {{- \frac{K_{dc}}{1 + {T_{Kdc} \cdot s}}} - \frac{1}{T_{dc} \cdot s}} \right)\left( {{{\hat{V}}_{D}^{*}(s)} - {{\hat{V}}_{D}(s)}} \right)}} & (3)\end{matrix}$

where,

V₂* represents a second axis voltage command;

V_(D)* represents a DC voltage command value;

V_(D) represents a DC voltage detection value;

s represents a variable of laplace transform;

K_(dc) represents a proportional gain;

T_(Kdc) represents a first-order lag time constant;

T_(dc) represents a integral time constant; and

^ represents a laplace transform.

Meanwhile, the command arithmetic circuit 151 in FIG. 3 calculates thedifference between the reactive power command value and the reactivepower value with a circuit combining a low pas filter characteristiccircuit and an integrating circuit similarly to the command valuearithmetic circuit 152 and generates the first axis voltage commandvalue.

For example, when the command value arithmetic circuit 151 and thecommand value arithmetic circuit 152 are constituted respectively withthe circuit in which the low pass filter characteristic circuit and theintegrating circuit are parallely-arranged, the first axis voltagecommand value and the second axis voltage command value are calculatedwith the following equation.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack & \; \\{\begin{pmatrix}{{\hat{V}}_{1}^{*}(s)} \\{{\hat{V}}_{2}^{*}(s)}\end{pmatrix} = {\begin{pmatrix}{\frac{K_{Q}}{1 + {T_{KQ} \cdot s}} + \frac{1}{T_{Q} \cdot s}} & 0 \\0 & {{- \frac{K_{dc}}{1 + {T_{Kdc} \cdot s}}} - \frac{1}{T_{dc} \cdot s}}\end{pmatrix}\begin{pmatrix}{{{\hat{Q}}^{*}(s)} - {\hat{Q}(s)}} \\{{{\hat{V}}_{D}^{*}(s)} - {{\hat{V}}_{D}(s)}}\end{pmatrix}}} & (4)\end{matrix}$

where,

V₁* represents a first axis voltage command (V);

V₂* represents a second axis voltage command (V);

Q* represents a reactive power command (var);

Q represents a reactive power value (var);

V_(D)* represents a DC voltage command value (V);

V_(D) represents a DC voltage detection value (V);

K_(Q) represents a first-lag gain of Q control;

T_(KQ) represents a first-order lag time constant (s) of Q control;

T_(Q) represents a integral time constant (s) of Q control;

K_(dc) represents a first-lag gain of DC voltage control;

T_(Kdc) represents a first-order lag time constant (s) of DC voltagecontrol;

T_(dc) represents a integral time constant (s) of DC voltage control;and

^ represents a laplace transform.

The single-phase voltage source AC/DC converter 11 operates as follows.When DC power is input from the DC terminal 21 side, the DC voltagedetection value V_(D) is increased. Since the error between the DCvoltage detection value and the DC voltage command value V_(D)* becomesnegative, the command value arithmetic circuit 152 operates so as toincrease the second axis voltage command V₂*. When the DC voltagecommand value V_(D)* is increased, the error against the DC voltagedetection value becomes positive. Accordingly, the command valuearithmetic circuit 152 operates so as to decrease the second axisvoltage command V₂*. In the command value arithmetic circuit 152 at thesecond axis voltage command V₂* side, the polarity of output againstinput is inverted. Meanwhile, relation between the first axis voltagecommand V₁* and the reactive power value is the same as in a case of PQcontrol. Accordingly, there is no inversion between input and output inthe command value arithmetic circuit 151 at the first axis voltagecommand V₁* side.

The single-phase voltage source AC/DC converter 11 further includes a DCcurrent detecting circuit 162 which detects the DC current value at theDC terminal 21. The command value arithmetic circuit 152 of the powercontrol circuit 150 adds the DC current value detected by the DC currentdetecting circuit 162 to the difference between the DC voltage commandvalue and the DC voltage detection value after the difference iscalculated by the low pass characteristic circuit 152 a, the integratingcircuit 152 b, or the parallel circuit 152 c. FIGS. 16 to 18 are viewsillustrating arithmetic at the command value arithmetic circuit 152 in acase of adding the DC current value.

FIG. 6 illustrates a schematic configuration diagram of a single-phasevoltage source AC/DC converter according to another embodiment.

The single-phase voltage source AC/DC converter 11 of the presentembodiment in FIG. 6 includes a fourth adder 69 which further addsoutputs from a filter current compensating unit 66, a PWM currentdeviation compensating unit 67, and a feedforward amplifier 68 to theoutput of the voltage controller 64 of the single-phase voltage sourceAC/DC converter 11 in FIG. 5. In this case, any of the single-phasevoltage source AC/DC converting circuits 40-1, 40-2 illustrated in FIGS.7 and 8 may be adopted as the single-phase voltage source AC/DCconverting circuit 40. Therefore, it is assumed that either of thesingle-phase voltage source AC/DC converting circuits 40-1, 40-2illustrated in FIGS. 7 and 8 is adopted in FIG. 6.

The filter current compensating unit 66 outputs a current compensationvalue defined so as to compensate the current loss in the single-phaseAC filter circuit 45 (FIGS. 7 and 8) in the single-phase voltage sourceAC/DC converting circuit 40. Accordingly, the single-phase voltagesource AC/DC converter 11 can compensate the current loss by setting thecurrent loss at the single-phase AC filter circuit 45 in FIG. 7 or FIG.8 previously in the filter current compensating unit 66 and adding tothe output vector from the voltage controller 64. Further, the PWMcurrent deviation compensating unit 67 outputs a current deviationcompensation value defined to compensate the current deviation of thesingle-phase AC output current from the single-phase voltage sourceAC/DC converting circuit 40. Accordingly, the single-phase voltagesource AC/DC converter 11 can compensate the current deviation bysetting the current deviation at the single-phase voltage source AC/DCconverting circuit 40 when the PWM command is set to zero commandpreviously in the PWM current deviation compensating unit 67 and addingto the output vector from the voltage controller 64. Further, thefeedforward amplifier 68 outputs as amplifying with a predeterminedfeedforward gain so that the value of the single-phase AC output currentdetected by the output current detecting circuit 34 is input tocompensate the current for the load at the AC terminal 22. Accordingly,the single-phase voltage source AC/DC converter 11 can generate thestable output voltage even when the load current is varied by detectingthe single-phase AC output current at the AC terminal 22 by the outputcurrent detecting circuit 34 and adding the value to the output valuefrom the voltage controller 64 via the feedforward amplifier 68.

The limiter 121 determines the superior limit and the subordinate limitof the first axis voltage command value 120-1 and the second axisvoltage command value 120-2 to prevent the first axis voltage commandvalue 120-1 and the second axis voltage command value 120-2 from beingexcessively input to the superior voltage control circuit 70.

As described above, the single-phase voltage source AC/DC converter 11in FIGS. 4 to 6 is capable of performing autonomous parallel operationas autonomously compensating the power deviation against the powersystem owing to including the frequency control circuit 50, the superiorvoltage control circuit 70, and the subordinate voltage control circuit60, while being capable of performing operation as being connected tothe power system as the voltage source owing to having the internalequivalent impedance. Accordingly, reliability of the device is improvedand dispersed arrangement can be adopted. In addition, in a case ofparallel operation with a plurality of devices, it is possible toperform the operation without limitation in the number of the devices.

Further, since the power control circuit 150 includes the command valuearithmetic circuit 152 and the second axis voltage command is generatedin accordance with the DC voltage detection value, the single-phasevoltage source AC/DC converter 11 can maintain the DC voltage at the DCterminal 21 at constant. Accordingly, the single-phase source AC/DCconverter 11 is capable of performing autonomous parallel operationwhile being capable of connecting a DC device of which outputting orrequiring DC power fluctuates to the DC terminal 21.

[Interconnection System]

Next, an interconnection system 301 including the single-phase voltagesource AC/DC converter 11 illustrated in FIGS. 4 to 6 is described. FIG.19 is a view illustrating a configuration of the interconnection system301. The interconnection system 301 includes the single-phase voltagesource AC/DC converter 11 and n (n is any positive integer) sets of DCdevices 203 which are connected to the DC terminal 21 of thesingle-phase voltage source AC/DC converter 11 via a DC/DC converters202 and which performs transmitting and receiving of DC power with theDC terminal 21.

The DC/DC converter 202 is a DC converter of a current output type. Forexample, when the DC device 203 is a solar cell, the DC/DC converter 202adjusts a voltage and a current so as to obtain the maximum power fromthe solar cell.

The DC device 203 is a DC energy source or a DC load. The DC energysource denotes a solar cell, a secondary cell, a fuel battery and thelike, for example. The DC load denotes a battery charger, for example.In the interconnection system 301, since the single-phase voltage sourceAC/DC converter 11 can maintain the DC voltage at the DC terminal 21 atconstant, the DC device 203 can be connected directly to the DC terminal21 via the DC/DC converter 202.

Here, in addition to transmitting and receiving of power between the DCdevice 203 and the power system, it is also possible that DC power isdirectly supplied to the DC device 203 being the DC load from the DCdevice 203 being the DC energy source in the interconnection system 301.Since the single-phase voltage source AC/DC converter 11 operates so asto maintain the DC voltage at the DC terminal 21 at a constant valueeven when the DC voltage from the DC energy source fluctuates, the DCload can receive power at a constant voltage.

Example

FIG. 20 shows a simulation result with a single-phase voltage sourceAC/DC converter at 200 V, 50 Hz, and 1 kVA. The single-phase voltagesource AC/DC converter includes the circuit in FIG. 4 as the commandvalue arithmetic circuit in the power control circuit. Then, the DCvoltage command value to be input to the power control circuit is set to330 V. Control parameters are set as “K_(dc)=0.6, T_(dc)=2 ms, andT_(Kdc)=0.25 sec”. Interconnection operation was performed in a state ofno load at the DC side in the beginning, and then, 1 kW of step-shapedDC load was applied at time 160 ms. The DC voltage at the DC terminal 21was decreased by 30 V after the load was applied. However, powerimmediately inflew from the AC terminal 22 side via the single-phasevoltage source AC/DC converting circuit 40, so that the DC voltagereturned approximately to the DC voltage command value at time 200 ms.Here, the receiving current waveform from the power system formed a sinewave as the power factor being 1.

The single-phase voltage source AC/DC converter of the present inventioncan be applied for an inverter for a dispersed power source such as asolar power generation inverter, a fuel cell inverter, a storage systeminverter and a wind power generation inverter with a DC link, arectifier, a static var compensator (SVC), and the like.

DESCRIPTION OF REFERENCE NUMERALS

11: single-phase voltage source AC/DC converter 21: DC terminal 22: ACterminal 30: phase difference generating circuit 31: output voltagedetecting circuit 33-1~33-3: terminal 34: output current detectingcircuit 35: phase delay single-phase AC generator 36: phase differencevoltage generator 38: current transformer 40: single-phase voltagesource AC/DC converting circuit 40-1, 40-2: single-phase voltage sourceAC/DC converting circuit 41: gate signal generator 42: single-phasevoltage source AC/DC converting unit 43: current detecting circuit 44:voltage detecting circuit 45: single-phase AC filter circuit 50:frequency control circuit 51: reference frequency setting unit 53: loopfilter 55: temporal integrator 56: second adder 57: generated electricalangle 58: third adder 60: subordinate voltage control circuit 61:reference voltage setting unit 62: first adder 63: third subtracter 64:voltage controller 65: second multiplier 66: filter current compensatingunit 67: PWM current deviation compensating unit 68: feedforwardamplifier 69: fourth adder 70: superior voltage control circuit 71a:first subtracter 71b: second subtracter 72a: first superior controlamplifier 72b: second superior control amplifier 73: first multiplier120-1: first axis voltage command value 120-2: second axis voltagecommand value 121: limiter 140: AC power measuring instrument 141:reference frequency circuit 142: voltage phase delaying circuit 143:current phase delaying circuit 144: power arithmetic circuit 145: activepower value measuring circuit 146: reactive power value measuringcircuit 147-1, 147-2, multiplier 147-3, 147-4: 148-1: adder 148-2:subtracter 149-1, 149-2: low pass filter 150: power control circuit 151:command value arithmetic circuit 152: command value arithmetic circuit152a: low pass characteristic circuit 152b: integrating circuit 152c:parallel circuit 153: adding circuit 154: adding circuit 161: DC voltagedetecting circuit 162: DC current detecting circuit 202: DC/DC converter203: DC device 301: inter connection system B1: superior command vectorB2: superior control block B3: ac-AVR block B4: ETM-PWM block B5: mainswitch

What is claimed is:
 1. A single-phase voltage source AC/DC converter,comprising: a single-phase voltage source AC/DC converting circuit whichhas internal equivalent impedance as seen from an AC terminal, forconverting power from a DC voltage source connected to a DC terminal tosingle-phase AC power to output from the AC terminal or for convertingsingle-phase AC power from a single-phase AC source connected to the ACterminal to DC power to output from the DC terminal in accordance with apulse width of a gate signal generated based on a PWM command; a phasedifference generating circuit, which has a phase delay single-phase ACgenerator for delaying a phase of a single-phase AC output voltage atthe AC terminal and generating a delay single-phase alternating voltage,for generating a phase difference voltage corresponding to phasedifference between the single-phase AC output voltage at the AC terminaland an internal electromotive voltage of the single-phase voltage sourceAC/DC converting circuit based on the delay single-phase alternatingvoltage; a superior voltage control circuit to which a first axisvoltage command for amplitude of the single-phase AC output voltage atthe AC terminal and a second axis voltage command for a single-phase ACfrequency at the AC terminal are input for outputting a voltage commandsignal generated so that the amplitude of the single-phase AC outputvoltage at the AC terminal approaches the first axis voltage command anda frequency command signal generated so that the single-phase ACfrequency at the AC terminal approaches the second axis voltage commandbased on the first axis voltage command, the second axis voltagecommand, the phase difference voltage from the phase differencegenerating circuit and the single-phase AC output voltage at the ACterminal; a frequency control circuit for determining an electricalangle of the internal electromotive voltage of the single-phase voltagesource AC/DC converting circuit to generate a generated electrical anglebased on a reference frequency of a single-phase AC output frequency atthe AC terminal, the frequency command signal from the superior voltagecontrol circuit, and an output signal from the phase differencegenerating circuit; a subordinate voltage control circuit for outputtinga signal generated so that the amplitude, the frequency, and the phaseof the single-phase AC output voltage approach a synthesized value of areference voltage of the single-phase AC output voltage at the ACterminal, the voltage command signal, and the generated electrical angleas the PWM command based on the single-phase AC output voltage at the ACterminal, the generated electrical angle of the frequency controlcircuit, and the voltage command signal from the superior voltagecontrol circuit; and a command value arithmetic circuit to which a DCvoltage command value to specify a voltage at the DC terminal is set andwhich obtains the second axis voltage command by detecting a DC voltagedetection value being the voltage at the DC terminal and calculatingdifference between the DC voltage command value and the DC voltagedetection value.
 2. The single-phase voltage source AC/DC converteraccording to claim 1, wherein the command value arithmetic circuitcalculates the difference between the DC voltage command value and theDC voltage detection value with a low pass characteristic circuit. 3.The single-phase voltage source AC/DC converter according to claim 2,wherein the low pass characteristic circuit of the command valuearithmetic circuit has characteristics of Equation 1 $\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack & \; \\{{{\hat{V}}_{2}^{*}(s)} = {{- \frac{K_{dc}}{1 + {T_{Kdc} \cdot s}}}\left( {{{\hat{V}}_{D}^{*}(s)} - {{\hat{V}}_{D}(s)}} \right)}} & (1)\end{matrix}$ where, V₂* represents a second axis voltage command;V_(D)* represents a DC voltage command value; V_(D) represents a DCvoltage detection value; s represents a variable of laplace transform;K_(dc) represents a proportional gain; T_(Kdc) represents a first-orderlag time constant; and ^ represents a laplace transform.
 4. Thesingle-phase voltage source AC/DC converter according to claim 1,wherein the command value arithmetic circuit calculates the differencebetween the DC voltage command value and the DC voltage detection valuewith an integrating circuit.
 5. The single-phase voltage source AC/DCconverter according to claim 4, wherein the integrating circuit of thecommand value arithmetic circuit has characteristics of Equation 2$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack & \; \\{{{\hat{V}}_{2}^{*}(s)} = {{- \frac{1}{T_{dc} \cdot s}}\left( {{{\hat{V}}_{D}^{*}(s)} - {{\hat{V}}_{D}(s)}} \right)}} & (2)\end{matrix}$ where, V₂* represents a second axis voltage command;V_(D)* represents a DC voltage command value; V_(D) represents a DCvoltage detection value; s represents a variable of laplace transform;T_(dc) represents a integral time constant; and ^ represents a laplacetransform.
 6. The single-phase voltage source AC/DC converter accordingto claim 1, wherein the command value arithmetic circuit calculates thedifference between the DC voltage command value and the DC voltagedetection value with a parallel circuit in which a low passcharacteristic circuit and an integrating circuit areparallely-arranged.
 7. The single-phase voltage source AC/DC converteraccording to claim 6, wherein the parallel circuit of the command valuearithmetic circuit has characteristics of Equation 3 $\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack & \; \\{{{\hat{V}}_{2}^{*}(s)} = {\left( {{- \frac{K_{dc}}{1 + {T_{Kdc} \cdot s}}} - \frac{1}{T_{dc} \cdot s}} \right)\left( {{{\hat{V}}_{D}^{*}(s)} - {{\hat{V}}_{D}(s)}} \right)}} & (3)\end{matrix}$ where, V₂* represents a second axis voltage command;V_(D)* represents a DC voltage command value; V_(D) represents a DCvoltage detection value; s represents a variable of laplace transform;K_(dc) represents a proportional gain; T_(Kdc) represents a first-orderlag time constant; T_(dc) represents a integral time constant; and ^represents a laplace transform.
 8. The single-phase voltage source AC/DCconverter according to claim 1, further comprising a DC currentdetecting circuit for detecting a DC current value at the DC terminal,wherein the command value arithmetic circuit adds the DC current valuedetected by the DC current detecting circuit when calculating thedifference between the DC voltage command value and the DC voltagedetection value.
 9. An interconnection system comprising: thesingle-phase voltage source AC/DC converter according to claim 1; and n(n is any positive integer) sets of DC devices which are connected tothe DC terminal of the single-phase voltage source AC/DC converter via aDC/DC converters so that DC power is transmitted to and received fromthe DC terminal.